1. Field of the Invention
Embodiments of the present invention relates to a communication system, and in particular to handover of a mobile device between at least two access nodes.
2. Description of Related Art
A communication device can be understood as a device provided with appropriate communication and control capabilities for enabling use thereof for communication with others parties. The communication may comprise, for example, communication of voice, electronic mail (email), text messages, data, multimedia and so on. A communication device typically enables a user of the device to receive and transmit communication via a communication system and can thus be used for accessing various applications.
A communication system is a facility which facilitates the communication between two or more entities such as the communication devices, network entities and other nodes. A communication system may be provided by one more interconnect networks. One or more gateway nodes may be provided for interconnecting various networks of the system. For example, a gateway node is typically provided between an access network and other communication networks, for example a core network and/or a data network.
An appropriate access system allows the communication device to access to the wider communication system. An access to the wider communications system may be provided by means of a fixed line or wireless communication interface, or a combination of these. Communication systems providing wireless access typically enable at least some mobility for the users thereof. Examples of these include wireless communications systems where the access is provided by means of an arrangement of cellular access networks. Other examples of wireless access technologies include different wireless local area networks (WLANs) and satellite based communication systems.
A wireless access system typically operates in accordance with a wireless standard and/or with a set of specifications which set out what the various elements of the system are permitted to do and how that should be achieved. For example, the standard or specification may define if the user, or more precisely user equipment, is provided with a circuit switched bearer or a packet switched bearer, or both. Communication protocols and/or parameters which should be used for the connection are also typically defined. For example, the manner in which communication should be implemented between the user equipment and the elements of the networks and their functions and responsibilities are typically defined by a predefined communication protocol.
In the cellular systems a network entity in the form of a base station provides a node for communication with mobile devices in one or more cells or sectors. It is noted that in certain systems a base station is called ‘Node B’. When a mobile device moves from a base station to another base station, handover techniques are used to ensure that the communication is not lost as a consequence of the move. There are many different techniques for processing signals for transmission between the base station and the user equipment, and the precise handover technique which is used depends on the access system.
Typically the operation of a base station apparatus and other apparatus of an access system required for the communication is controlled by a particular control entity. The control entity is typically interconnected with other control entities of the particular communication network. Handover management is typically provided by an appropriate handover control entity of the cellular communication system. The handover controller typically provides a centralised control of handovers in a radio access network so as to appropriately control the handover in different cells of the access network. For example, a radio network controller (RNC) centrally manages handovers in Universal Terrestrial Radio Access Networks (UTRAN) and a base station controller (BSC) manages the handovers in GSM (Global System for Mobile) EDGE (Enhanced Data for GSM Evolution) Radio Access Networks (GERAN).
However, it has been proposed that various control functions that have been typically handled by a centralised controller can also be handled in a distributed manner. This kind of distributed architecture is sometimes referred to as a “flat architecture”. In view of handover management this means that there is no central node in a radio access network, but the handover control is distributed to be taken care of by a base station and associated local control functions thereof.
A non-limiting example of such architectures is a concept known as the Evolved Universal Terrestrial Radio Access (E-UTRA). An Evolved Universal Terrestrial Radio Access Network (E-UTRAN) consists of E-UTRAN Node Bs (eNBs) which are configured to provide base station and control functionalities of the radio access network. The eNBs may provide E-UTRA features such as user plane radio link control/medium access control/physical layer protocol (RLC/MAC/PHY) and control plane radio resource control (RRC) protocol terminations towards the mobile devices. The eNBs interface to an E-UTRAN access gateway (aGW) via a so called S1 interface, and are inter-connected via a so called X2 interface.
However, a flat architecture provides no central management entity for managing handovers. This means that some information that would be available in a central node such as the UTRAN RNC or GERAN BSC may disappear when the mobile device moves from one E-UTRA access node to another. This may result inefficiencies in the mobility and radio resource management. In extreme cases lack of this information may even result lost data and failed handovers.